The present invention relates to a system and a method for microlithographic writing on photosensitive substrates, and specially printing of patterns with extremely high precision, such as photomasks for semiconductor device patterns, display panels, integrated optical devices and electronic interconnect structures. The terms writing and printing should be understood in a broad sense, meaning exposure of photoresist and photographic emulsion, but also the action of light on other light sensitive media such as dry-process paper, by ablation or chemical processes activated by light or heat. Light is not limited to mean visible light, but a wide range of wavelengths from infrared to extreme UV.
A system and method for microlithographic writing of a substrate is previously known from e.g. EP 0 467 076 by the same applicant. An example of a system for microlithographic writing, as is shown in FIG. 1, comprises a light source 1, such as a laser, a first lens 2 to contract the light beams, a modulator 3 to produce the desired pattern to be written, the modulator being controlled according to input data, a reflecting mirror 4 to direct the beams towards the substrate 6, and a lens 5 to contract the beams before they reach the substrate. The mirror 4 can be used for a scanning operation to scan the beam over scan lines at the substrate. Several functionally equivalent scanners such as acusto-optic deflectors etc. could also be used. Further, the substrate is preferably arranged on a object table. Two-dimensional relative motion between the lens 5 and the table (stage) is provided and controlled by servo systems. For example the object table could be movable in at least two orthogonal directions, by means of two electrical servo motors.
However, a problem with such known writing systems are that the emission direction of the laser is not constant, but suffers from significant direction variations. Further, vibrations from the water cooling system of the laser are transmitted into the laser, and affects the emitted light beam. The laser beam may also be affected by turbulence and the like in the air, which is particularly likely to occur when the laser becomes warm. As a result there is a deviation between the actual laser light direction and the intended direction, and consequently the precision in the writing on the substrate is decreased.
It is therefore an object of the present invention to provide a system in which the above mentioned problems with the prior art is solved.
This object is achieved with a system according to the appended claims.
According to the invention a system for microlithographic writing of high precision patterns on a photosensitive substrate (6) is provided, the system comprising a light source (1), preferably a laser, a computercontrolled light modulator (3) and a lens to contract the light beam from the light source before it reaches the substrate. Further, it comprises means for controlling the position of incidence of the beam on the substrate, a detector for detecting the deviation from the intended position of incidence of the beam on the substrate, and correcting means for controlling the position controlling means in accordance with the detected deviation to diminish position errors at the substrate related to said deviations. Preferably the detector detect deviations from the intended position of the beam before it reaches the modulator.
According to this system there is at least a compensation for deviations in the light beam that are generated ahead of the modulator. Since most deviations are generated in the laser or close to the same, most such deviation errors are hereby taken care of.
Further, according to the invention the detector detects deviations from the intended position of incidence of the beam on the substrate. This could either be done by a direct measurement or by measuring in a plane being optically equivalent with the image area on the substrate.
In a preferred embodiment the position controlling means comprises small servos attached to a reflecting mirror, reflecting the light beam before it reaches the substrate, to control the position of the same, and preferably before it reaches the modulator. Hereby the correction of the beam is made before the light reaches the modulator, and hence the image that is written on the substrate is essentially an exact reproduction of the image generated in the modulator.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.